The conventional art solenoid valves of this kind include, for example, a solenoid valve shown in FIG. 7. FIG. 7 is a schematic construction diagram in section of the conventional art solenoid valve.
The solenoid valve 200 includes a solenoid portion 200A, and a valve portion 200B.
Here, in the illustrated example, the valve portion 200B represents a spool valve type capable of controlling an inflow rate and an outflow rate of a fluid by varying a cross-sectional area of an opening of the valve in accordance with a stroke of a spool.
The solenoid portion 200A is generally provided with a substantially cylindrical coil 203 adapted to generate a magnetic field when it is energized, a plunger 201 magnetically attracted to a center post 202 by the magnetic field generated in the coil 203, a rod 204 connected to the plunger 201 so as to transmit a driving force of the plunger 201 to the valve portion 200B (spool specifically), and a substantially bottomed cylindrical metal sleeve 205 provided so as to cover the outer surfaces of the plunger 201 and center post 202 for the purpose of positioning (centering) the plunger 201 and center post 202.
Besides, the solenoid portion 200A is provided with an upper plate 206 forming a magnetic path, a molded section 207 in which the coil 203 is integrally molded, and a metal case member 208 in which these members are held.
Also, the center post 202 is provided with a plate portion 202a extended to radial direction in the vicinity of an opened end of the sleeve 205. At the end surface of the molded section 207 which is on the side of the plate portion 202a, an inclined surface 207a is provided. These plate portion 202a, inclined surface 207a and an inner circumferential surface 208a of a case member 208 form a substantially cross-sectionally triangular annular space.
This annular space is provided therein with a first O-ring 209, which closely contacts the plate portion 202a, inclined surface 207a and inner circumferential surface 208a of the case member 208. Thus, the entry of the water (contaminants), which causes a poor insulation of the coil and the short-circuiting thereof, from the outside into an inner portion (bobbin) of a body of the solenoid valve 200 is prevented.
The cause of the poor insulation of this coil or the cause of the short-circuiting thereof will now be described in detail. The portion of the center post 202 and that of a valve sleeve 202c at which these two parts are fixed to each other by case-caulking are liable to cause deformation, which results in a gap between these parts.
Moreover, at the metal upper plate 206 and an integrally molded portion of a resin provided on the periphery thereof, a gap between these portions occurs due to the expansion and contraction thereof ascribed to the variation of the temperatures, because the metal and resin are comparatively different in a coefficient of linear expansion.
Therefore, the water flows from the outer side, and through the gap in the case caulked portions, and the water then flows from this gap in the case caulked portions and through the gap between an inner circumferential surface of the case and an outer circumferential surface of the molded portion, and/or from the gap between the inner circumference of the bobbin and the outer circumference of the sleeve and through the gap between the upper plate and resin portion to enter the coil portion.
The center post 202 is provided in an outer circumference thereof with an annular groove 202b, in which a second O-ring 210 is also provided. Since the second O-ring 210 closely contacts an inner circumference of the sleeve 205, a fluid (oil in a hydraulic pressure control-dedicated) in the solenoid valve body is prevented from flowing to the outside.
The operation of the solenoid valve 200 will now be described.
The plunger 201 is formed so that when the plunger is in a normal condition, i.e., when the coil 203 is not energized, the plunger 201 is positioned in the direction in which the plunger is separated from the center post 202.
The plunger is generally formed so that the plunger is urged by an urging member, such as a spring and the like in the direction in which the plunger 201 is separated from the center post 202. In the illustrated example, a spring for urging the spool toward the solenoid portion 200A is provided, by which the plunger is separated from the center post 202 via the spool.
Also, when the coil 203 is energized, the coil 203 generates a magnetic field and a magnetic path is formed. The plunger 201 is then magnetically attracted to the center post 202.
Accordingly, a magnetic force can be controlled in accordance with a level of the electric current supplied to the coil 203. When a quantity of movement of the plunger 201 is thereby controlled, a quantity of stroke of the spool can be controlled. This enables a flow rate of the fluid to be controlled, and pressures of various kinds of fluids to be controlled such as a hydraulic pressure control.
However, in the above-described conventional art, the following problems occurred.
As described above, between the inside and the outside of the main body of the solenoid valve 200 in order to prevent the entry of the water (contaminants), which causes a poor insulation of a coil and the short-circuiting thereof, and the leakage of the fluid from the inner portion, it was necessary that two O-rings (first O-ring 209 and second O-ring 210) be provided.
Incidentally among the members constituting the solenoid valve body 200, the center post 202, sleeve 205 and case member 208, etc. are made of a metal, while the molded portion 207, and bobbin around which the coil 203 is wound, etc. are made of a resin.
In particular, the first O-ring 209 prevents the water on the outer side of the valve from flowing from the caulked portion of the case, and through the gap between the outer circumference of the mold coil and the inner circumference of the case and/or a gap between the inner circumference of the bobbin and the outer circumference of the sleeve, and then through the gap between the upper plate and resin (mold) to enter the inner portion of the coil, and thereby prevents the poor insulation and short-circuiting of the solenoid from occurring.
Also the second O-ring 210 is provided mainly for the purpose of preventing the leakage of the fluid from the inner portion.
This is because the leakage of the fluid (oil) in the direction of an arrow A in FIG. 7 causes the fluid to permeate and leak into the connector portion, etc. and results in the malfunctions of gathering the oil in the connector, etc. if the second O-rings 210 is not provided. The leakage is caused by the gaps between the metal sleeve 205 and molded portion 207, between the metal sleeve 205 and bobbin, and between the metal upper plate 206 and bobbin because gaps readily occur between the metal members and resin members as mentioned above.
Under the circumstances, the second O-ring 210 closely contacting the metal center post 202 and sleeve 205 delivers a high sealing performance.
Although a sufficient sealing performance is thus displayed owing to the use of the two O-rings, an increase in the number of parts and the complication of the construction were invited.
It is necessary that an annular groove 202b be provided in the center post 202 for fitting the second ring 210 therein, a magnetic flux is hard to be formed between the portion which is provided with the annular groove 202b and coil 203. This constituted a factor of causing the solenoid valve 200 itself to be enlarged for securing a required magnetic flux.
An object of the present invention is to provide a solenoid valve which has attained the simplification of the construction, the miniaturization and the reduction of the weight while the sealing performance between inner and outer of the main body is maintained.